# Cover Crop calculator

Paper instructions:
Scenario I: calculating the cost of PAN
Here is the scenario. Tom grows 30 acres of organic vegetables and just got a visit from his friend Jim who sells organic fertilizers. Jim told him about a new blended organic fertilizer with 7% total N, 2.5% P205 and 2.5% K20. It is 96% dry matter and costs \$800/ton. You also know that urea is selling for \$0.17/pound.
2. On the fertilizer analysis page, add an entry of ‘Friends fertilizer’ and add values in the appropriate yellow colored column.
3. Then go to the “Cost Comparisons” tab on the spreadsheet, enter the cost/lb (=800/2000)

1.1 What is the cost per pound of dry matter?
1.2 In one field he needs plant-available nitrogen (PAN) only, would you recommend he buy this new fertilizer for that field, why or why not? What would you recommend as an alternative to his friend’s fertilizer and why?

Scenario II: Calculating cover crop contribution to N for plant growth
Jerry is a processed vegetable grower in the mid-Willamette Valley who produces beans, sweet corn, broccoli, and cauliflower. At the end of the season the residual soil nitrate-N levels in a 100 acre field that had been planted to broccoli was 30 mg/kg soil. This corresponds to ~120 lbs N/A in the top foot of soil. To prevent that nitrate from being lost to leaching during the winter, he decided to plant a nitrogen (N) scavenging, cereal rye cover crop at a rate of 70 lbs/A. Before mowing and discing under the rye he wanted to know how much N the cover crop had removed from the soil. To do so he sampled a 1 m2 area (11 sq ft), which contained 2,500 g fresh foliage. He then sent a subsample off to the lab for analysis. The lab analysis showed that it had 3.7% total N, 44% total C, and 13.4% dry matter.
Steps
1. Go to the Cover crop analysis page and enter the above appropriate date in the yellow columns.
2.1 How much dry matter and total N did the cover crop produce?
2.2 What was the C:N ratio?
2.3 What percentage of N present in the soil prior to sowing the cover crop was removed by the rye cover crop?
2.3 After incorporating the rye, how much plant available PAN is estimated to be available for the following crop?

On the day Jerry was planning on mowing and discing the cover crop, his tractor broke down. Although he had the tractor fixed by the next day, a storm system moved in and he was unable to deal with the cover crop for 2 weeks because the soils were too wet. Because the cover crop continued to grow over this period, he decided to harvest another 1 m2 area, which had 3,600 g of fresh foliage. The lab analysis showed that it had 2.9% total N, 45% total C, and 13.6% dry matter.

2.4 How much dry matter and total N did the cover crop produce?
2.5 What is the C:N ratio of this older rye cover crop?
2.6 After incorporating the rye, how much plant available PAN is estimated to be available for the following crop?
2.7 What accounts for the difference in PAN between the two sampling dates?
2.8 What is the advantage of killing the cover crop when it is younger?

Jerry will plant sweet corn in this field. Usually he applies 280 lbs urea/A (urea is 46% N) to grow this crop. Based on the PAN estimate from the first date that he sampled the cover crop, he decides to reduce his fertilizer applications.
2.9 How much urea should he apply to the crop accounting for the cover crop PAN?
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